In a conventional windmill, there are provided with a plurality of fan blades fixed on a transmission shaft to be blown by wind for producing power, which however, if being made as flat shape, will not efficiently "catch" the wind since the wind will "escape" from the flat edges of a fan blade, to thereby reduce the efficiency of power generation.
When the natural wind blows very strongly, such a strong wind may cause damage or influence the stability of the power generator and a clutch means to automatically brake the fan shaft of the power generator will be expected for the safety purpose of such a windmill.
The present inventor has known these phenomena of a conventional windmill and invented the present windmill.